Method of rolling strips of metal



United States Patent 3,195,333 METHQD @F ROLLENG TRIPS 0F METAL Louis McDaniel, Highland, ind, assiguor to Inland Steel Company, Chicago, Ill., a corporation of Delaware No Drawing. Filed Jan. 7, 1963, Ser. No. 249,593 6 Claims. ((Il. 72-46) The present invention relates generally to a method and means for reducing the thickness of a plurality of superimposed strips of ferrous metal by pressure rolling said strips, and more particularly to an application thereof to an improved method and means of forming strips of ferrous metal having a protective metal applied to only one side of said strips.

In processing steel from a hot ingot into a thin rolled steel strip, it is customary to form an intermediate hot mill band having a thickness of about 0.250 inch which is further reduced in thickness by one or more hot and cold reduction rolling operations to produce a steel strip of the desired dimensions. In some instances it has been found desirable to superimpose one hot mill band on top of another hot mill band and simultaneously reduce the thickness of both bands by subjecting the two bands simultaneously to pressure rolling with or without first welding their lateral edges or leading edges together, as when a tubular structure is desired, or when only the outer sur faces of the superimposed strips are to be coated with a protective metal, such as zinc or aluminum.

When two hot mill bands or other steel strips are superimposed and subjected to a series of hot and/ or cold pressure rolling operations to significantly reduce the thickness thereof, the two hot mill bands frequently are pressure welded together so that the strips cannot be readily separated or, when separated, the surfaces of the strips which were contiguous have unsatisfactory surface characteristics.

It is therefore an object of the present invention to provide an improved method and means of pressure rolling superimposed steel ingots or strips to reduce the thickness thereof which avoids causing the contiguous surfaces of the strip to be pressure welded together or producing on contiguous surfaces of the strip undesirable surface characteristics.

It is a further object of the present invention to provide an improved method and means of producing strips of metal by pressure rolling superimposed strips of metal to reduce the thickness of said strips.

It is also an object of the present invention to provide an improved method of producing metal sheets or strips having a satisfactory cold rolled surface by superimposing two or more hot mill bands of ferrous metal with the hot mill scale and oxides remaining thereon and subjecting said bands to hot and cold pressure rolling to reduce the thickness thereof without pressure welding said bands together and without imparting undesirable surface characteristics to the contiguous surfaces of the reduced strips.

It is a still further object of the present invention to provide an improved and more economical method of providing strips of metal with a coating of a protective metal on one side only.

It is another specific object of the present invention to provide an improved method of producing a galvanized or aluminized steel strip having a zinc or aluminum coating on only one side thereof.

Other objects and adaptation of the present invention will be apparent from the detailed description and claims to follow.

3,195,333 Patented July 20, 1965 It has been found that the foregoing objects can be achieved by applying to contiguouus surfaces of strips of metal, such as a steel hot mill band, before superimposing two or more strips and pressure rolling, a stopweld coating composition comprising a ground coat slip of the type used in the porcelain enamel industry. The ground coat slip coating is applied to one or more surfaces of the metal strips and the slip coating allowed to dry before superimposing the metal strips and pressure rolling, preferably by a combination of hot and cold rolling operations. It has been unexpectedly found that in addition to preventing pressure welding of the contiguous surfaces of the strips, a clean, substantially smooth metal surface is obtained on separation of the-strips coated with a vitreous enamel ground coat slip even without having removed the hot mill scale or rust from the surfaces of the hot mill band or strip before applying the ground coat slip coating. The vitreous enamel ground coat slip on heating appears to completely absorb the hot mill scale, and on further heating of the strips the enamel is burned off to form a vitreous enamel layer which effectively prevents the contiguous surfaces being pressure welded during a subsequent pressure rolling operation. When the strips are subsequently rolled at a temperature below the melting point of the enamel, the vitreous enamel layer is ground to a fine dust so that the strips can be readily separated and the finely divided enamel removed to provide a' clean smooth metal surface.

It is within the purview of the present invention to employ any conventional vitreous or porcelain enamel ground slip coating composition which on heating to a temperature below the melting point of the metal during or prior to a hot rolling operation fuses to form a glass or enamel, The major components of the vitreous or porcelain enamel steel ground coat frit which are useable in the present invention to form a suitable ground coat slip coating are feldspar (2530% by weight), borax (25-30% by weight) and quartz (15-30% by weight), along with other conventional minor ingredients, including soda ash (510% by weight), sodium nitrate (1-5% by weight), fluorspar (2-10% by weight), and, of course, the usual small amounts of an essential adherence promotingmetal oxide, such as cobalt oxide, nickel oxide, molybdenum oxide or an equivalent adherence promoting metal oxide used in a ground coat slip. Other sources of silica and fluxing agents for use in producing a vitreous enamel can also be used in place of the above specified major components without departing from the present in vention, as those skilled in the vitreous enameling art will readily appreciate. A typical composition of porcelain enamel ground coat frit which can be used in the present invention is as shown in the following Table I:

Percent Feldspar 31.0 Borax 31.0 Quartz 20.0 Soda ash 7.0 Soda nitrate 3.0 Fluorspar 6.0 Cobalt oxide .5 Manganese oxide 1.5

The foregoing frit is prepared in the usual manner by mixing the ingredients, melting the mixture and running the melt into a Water bath.

An enamel slip is formed from the foregoing frit by grinding parts of the above hit in a suitable ball mill Melted composition:

3,1es,a

with the usual flotation ingredients. A typical slip composition is shown in the following Table II:

Parts by weight Frit 100 Clay 6 Borax .25 MgCo .129 NaNO .125 Bentonite .125

Water 45 The slip which can be applied to one or both sides of a steel strip or hot mill band by brushing, spraying or dipping to form a coating thickness of about 0.005 inch when dry, although substantially thicker coatings can also be used. It will be understood, of course, that the frit can be admixed and ground with other conventional slip ingredients, and used in'varying proportions to form a suitable steel ground-coat slip for use in the present invention. For example, the clay can be used in a proportion of from about 1 to 10% by weight, and the remaining ingredients used in similarly varying proportions. As an alternate slip composition 100 parts of the frit of Table I can be mixed with 7% by weight clay, 0.25% sodium aluminate, 0.25% sodium nitrite, and 40% water.

The 'melt composition and empirical formula of the enamel resulting from .the, slip of Table II is as shown in the following Table III:

Percent N320 .-V---'- 11.9 K 6 0 Ca() O A1 0 9.8 B 0 13.2 SiO 48 4 C00 0.6 M1102 Fluorides 3.4

Empirical formula:

v K 0 .135 CaO .257 A1 0 .196 B 0 .538 SiO 2.212 CoO .021 MnO .057 Fluorides .254

After the enamel slip coating is applied, for example, to one surface of two hot mill bands (each .250 inch thick) with the bands still having the mill scale thereon and the coating allowed to dry, the coated surfaces of the bands are placed in contact, heated to a temperature of about 2500 F. and hot rolled down to .18 inch gauge in conventional sheet steel rolling apparatus. Thereafter the strips are cold reduced to 0.080 inch gauge thickness during which the enamel coating is finely ground or pul. v d- Th? esultin rolled strips can. be immediately separated and th 1 .1 Surfacesthereof have highly satisfactory substantially smooth cold rolled surface characteristics.

l'l can be made in the. foregoing frit and slip composition without departing from the inventive concept, as one skilled in the art of vitreous porcelain enameling l rea ly appreciate.

One application of the present invention is in forming a tube-like steel structure from metal strips, such as hot mill bands Thus, two hot mill bands having the hot mill scale remaining thereon can be coated by spraying on one surface thereof a sutlicient quantity of a vitreous or porcelain enamel ground coat slip with a major proportion thereof comprised of feldspar, borax, and quartz as an aqueous suspension to form a coating when dry having a thickness of about .005 inch. The coated bands are superimposed with their dry coatingsin contact and the oppositely disposed lateral edges are welded together before rolling. The bands are then hot rolled at a temperature at least above the fusion point of the enamel slip and below the melting point of the metal so that a vitreous enamel coating is formed on cooling, andthereafter the bands are cold rolled to the final gauge thickness desired during which rolling the enamel coating is finely ground. The sections of the bands or rolled strips between the welded edges are separated or expanded to form the desired tube-like form and subjected to any desired or suitable abrasive cleaning operation for removing all of the ground enamel particles.

A further specific application of the present invention is in a process of producing steel strips having only one side coated within protective metal, such as one side aluminized and galvanized steel strips, directly from the hot mill bands having a thickness of about .250- inch. In the latter application, two hot mill bands having the mill scale thereon are spray coated on one side thereof with a porceiain enamel sheet steel ground coat slip having the composition of Table II with the major proportion thereof comprised of feldspar, borax, and quartz. After drying, the coated sides of the steel strips are placed together and the leading and lateral edges of the strips are welded together priorto rolling. The assembly is then subjected to conventional hot rolling at an elevated temperature (i.e. 2400 P.) which is above the fusion point of the slip coating to reduce each strip to a thickness of aboutv .180 inch, followed by pickling the outer surfaces thereof to remove surface scale, and cold reduction rolling to a final thickness of about 0.080 inch.

The steel strips processed in the foregoing manner with only the lateral and leading edges thereof remaining welded together are then passed through a hot dip galvanizing bath or line of a conventional type to apply a zinc coating to the exposedouter surfaces of the strips with the inner surfaces thereof remaining ungalvanized.

After leaving the galvanizing bath the leading. and lateral welded edges are sheared off and the steel strips are readily separated into two sheets with a protective coating of zinc on one side only, the other side being uncoated and having a satisfactory cold rolled surface.

Among the other applications and uses of the herein disclosed method and parting agent are the production from relatively thick metal ingots'or strips of thin gauge metal sheets, tubular parts, expanded metal parts, and the like structures wherein at least certain portions of two or more oppositely disposed metal surfaces are to be separated after pressure rolling superimposed metal ingots or strips.

It will be evident to those skilled in the art that other metals beside ferrous metals which tend to be pressurewelded when subjected to hot or cooled rolling operations can be used in the herein disclosed process. And, where it is not necessary to remove surface oxides from the metal strip during the process, it will be suitable to use any slip coating which provides on heating to a convenient temperature below the melting point of the metal, a vitreous enamel layer which on subsequent rolling can be ground to a finely divided form and removed from the metal surface.

I claim:

1. In a method of rolling metal strips by subjecting said strips to a hot rolling operation followed by rolling said strips at a reduced temperature, the improvement which comprises; applying to at least one surface of a metal strip a vitreous enamel ground slip coating, placing the coated strip in superimposed relationship with another metal strip with said coating interposed between said strips, hot roiling said strips while heated toa temperature at which said slip coating fuses and which on cooling forms a vitreous enamel coating, rolling said strips at a temperature below the fusion point of said ground coat slip to fragment said enamel coating, and thereafter separating said strips.

2. In a method of rolling metal strips by subjecting said strips to a hot rolling operation followed by rolling said strips at a reduced temperature, the improvement which comprises; applying to at least one surface of a metal strip a vitreous enamel ground coat slip coating and allowing said slip coating to dry, placing the coated strip in superimposed relationship with another metal strip having said coating interposed between said strips, hot rolling said strips while heated to a temperature at which said ground coat slip coating fuses and which on cooling forms a vitreous enamel layer, rolling said strips at a temperature below the fusion point of said enamel layer to fragment said enamel layer, and thereafter separating said strips.

3. In a method of producing metal strips in which a plurality of superimposed ferrous metal strips are subjected to hot and cold rolling operations to reduce the thickness of said strips and provide a cold rolled surface on one side thereof and having a smooth residue-free surface on the opposite side, the improvement comprising; applying to one surface of a ferrous metal strip a vitreous enamel ground coat slip coating and allowing said slip coating to dry, placing said strip in superimposed relationship with another ferrous metal strip with said slip coating interposed between said strips, hot mill rolling the thus superimposed strips to effect a reduction in thickness of each said strip at a temperature at which the said ground coat slip fuses and to form on cooling below the melting point thereof a vitreous enamel layer, cold rolling said superimposed strips at a temperature below the fusion point of said enamel layer to grind said enamel layer into a finely divided form, and thereafter separating said strips having smooth surface free of adhering surface residues.

4. A method as in claim 3, wherein said strips are ferrous metal hot mill bands having normal surface scale and oxides thereon.

5. A method as in claim 3, wherein said slip coating before hot mill rolling has a thickness of at least about .005 inch.

6. A method as in claim 3, wherein said ground coat slip is prepared by grinding a vitreous enamel ground coat frit composition comprised essentially of feldspar, borax and quartz with a small amount of clay as a flotation agent to form an aqueous suspension which on heating to a temperature of about 2400 F. fuses to form a vitreous enamel layer.

References fitted by the Examiner UNITED STATES PATENTS 2,120,496 6/38 Hanger 29528 2,759,247 8/56 Grenell et a1. 29-1573 2,983,994 5/61 Johnson 29528 2,991,550 7/61 Block c- 29529 3,029,155 4/62 Maier et al 29-423 3,047,943 8/62 Wilkins 29-423 WILLIAM J. STEPHENSON, Primary Examiner.

MICHAEL V. BRINDISI, Examiner. 

1. IN A METHOD OF ROLLING METAL STRIPS BY SUBJECTING SAID STRIPS TO A HOT ROLLING OPERATION FOLLOWED BY ROLLING SAID STRIPS AT A REDUCED TEMPERATURE, THE IMPROVEMENT WHICH COMPRISES; APPLYING TO AT LEAST ONE SURFACE OF A METAL STRP A VITREOUS ENAMEL GROUND SLIP COATING, PLACING THE COATED STRIP IN SUPERIMPOSED RELATIONSHIP WITH ANOTHER METAL STRIP WITH SAID COATING INTERPOSED BETWEEN SAID STRIPS, HOT ROLLING SAID STRIPS WHILE HEATED TO A TEMPERATURE AT WHICH SAID SLIP COATING FUSES AND WHICH ON COOLING FORMS A VITREOUS ENAMEL COATING, ROLLING SAID STRIPS AT A TEMPERATURE BELOW THE FUSION POINT, OF SAID GROUND COAT SLIP TO FRAGMENT SAID ENAMEL COATING, AND THEREAFTER SEPERATING SAID STRIPS. 